The present invention relates generally to gear extruders, and more particularly to a gear extruder for the plasticizing and homogenizing of rubber mixtures.
It is already known to use gear pumps configured as gear extruders for plasticizing plastic granules (DE-OS 24 38 013). It has already become known to use gear extruders for plasticizing and homogenizing rubber mixtures, in which the gear extruders are fed with cold rubber strips. Such use of rubber extruders is described in the trade publication, xe2x80x9cGummi, Fasern, Kunststoffexe2x80x9d 11/96, pages 880 and 881.
It has now been found that, as long as it is possible to stabilize the fluctuating bulk stream, gear extruders are also suitable for extruding, by means of a mold disposed on the gear, to extrude not only preliminary shapes for further working, but also to extrude finished profiles. Especially in the production of finished profiles it is necessary, however, to remove to the greatest possible extent the volatile components and the moisture contained in the rubber mixture. This, however, is not possible with the conventional gear extruder.
The invention is addressed to the problem of designing a gear extruder such that, during the extrusion process, the volatile components contained in the rubber mixtures, and the moisture, can be thoroughly removed.
According to the invention, it is arranged that, in the extruder housing, at the ends of the teeth of the gears, in an area in which the teeth disengage from one another and/or that at the input end of the teeth filled with the rubber mixture, in an area extending at the input side over no more than half of the circumference of the chambers, gas vent ports are provided in the extruder housing. By such an arrangement of gas vent ports in areas of no pressure and areas of a slight excess pressure it has become possible to ventilate the rubber mixture such that volatile components and moisture contained in the mixture can be eliminated, and such that the rubber mixture cannot enter into the gas vent ports and clog them.
According to a preferred embodiment of the invention, the gas vent ports are disposed on one side of the gears, and the teeth of the gears are of a helical pattern and are disposed so that the rubber mixture is moved away in the teeth from the gas vent ports. This assures that the rubber mixture being extruded cannot enter the gas vent ports. With the teeth of the gears thus configured it is even possible very effectively to outgas the rubber mixture that is in the teeth, even in areas of low overpressure.
The same effect is obtained if the gas vent ports according to another preferred embodiment of the invention are disposed on both sides of the gears and if the teeth of the gears are configured as herringbone gears and are oriented such that, in the teeth, the rubber mixture is shifted away from the surfaces on which the gas vent ports are disposed. Here too it is brought about that the rubber mixture cannot enter into the gas vent.
Within the scope of the invention it is furthermore provided that the gas vent ports which are formed in the area in which the teeth disengage are in the form of bores. The result is an especially simple solution as regards manufacture.
In a further aspect of the invention, the gas vent ports disposed in the circumferential part of the chambers may be configured as pockets extending over a part of the circumference and corresponding to several teeth of the gears. In such a configuration it is possible to outgas the rubber mixture effectively over a large area.